Method of recovering hydrocarbons



Patented Feb. 17, 1942 METHOD OF RECOVERING HYDROCARBONS Gerald -W.McCullough, Bartlesville, Okla., assignor to4 Phillips PetroleumCompany, a-corporation cf Delaware Application September 26, 1938,Serial No. 231,820

1 Claim.

Thisinvention relates to a processl of separating gases and vapors byselective absorption. More particularly, this invention relates to acombination absorption System using two` absorbents of' differentmolecular weights, one absorbent being the usual mineral seal oil orother conventionalv absorbent, and the other consisting of the lightercomponents of new mineral seal oil and the liquefied heavier componentsof the absorbed gases or vapors.

An important object of the present invention is to provide an absorptionprocess wherein a more complete recovery of the valuable constituents isaccomplished without increasing the 'amount of absorbent or thedistillation apparatus.

A further important lobject of the present invention is to provide anabsorption process having two absorbents, one being lighter than theother and being formed of the light ends of the other plus the liquefiedheavier constituents of the vapors being recovered.

A further important object of the present invention is to utilize as anabsorbent, a liquid, all of which is separated inthe dephlegmator of thedistillation end of the absorption system cycle and is hereinaftercalled oil reflux.

In the usual practice of recovering gasoline from natural gas, in whichthe absorption system comprises the conventional absorber, still, andldephlegmator, the fractions knocked out in the dephlegmator are sentfrom the dephlegmator back to the still. Thus, a particular advantage ofthe present system is a utilization of the oil reflux from thedephlegmator for an absorbent instead of just circulating it through thestill and dephlegmator, thereby getting more eflicient recovery.

Other advantages of the present combination absorption system over theconventional system mentioned above are; greater absorption of valuablelight components of the inlet gas because of the increased total oilcirculation to the absorber; greater absorption of valuable lightcomponents of the inlet gas because f the decreased averagemolecularweight of the total absorbent; a decrease of oil necessary atthe top of the absorber should it be desired to maintain the sameabsorption of valuable components of the inlet gas, because of the lowermolecular weight of the oil reflux used as absorbent;A the ease ofinstallation in present plants by the insertion of a pump and coolingcoils for the oil reux; and the ability to be better utilized at maticelevation of an apparatus suitable for carrying out the presentinvention.

In the drawing', Il denotes an absorber `of usual type receiving gasfrom .a line 2. Absorption oil such as mineral seal oil is supplied tothe upper part of absorber I through a line 3. The enriched absorptionoil is run out of absorber I through a line 4 and by means of pump 5 ispassed through heat exchangers 6 and I and discharged into vent tank 8.From tank 8, the rich oil is passed through preheater 9 and into theupper part of a steam still I0. Steam enters still I@ through steaminlet line 21, While the vapors and steam from still l0 pass throughline I I into dephlegmator I2. Vapors that are liberated from vent tank8 are also passed into dephlegmator I2 through pipe line 8a.

The stripped or lean oil flows from still IIJ through line I3, throughheat exchanger I into lean oil surge tank I4. From tank I4, the lean oilis pumped through line I5 by pump I6, through heat exchanger 6 andcooler I'I to the absorber Ithrough line 3.

Water is introduced into the top of dephlegmator I2 through pipe line I8and withdrawn therefrom by a pipe Isa through cooler I9 by pump 20 andback to the top of the dephlegmator through the pipe I8 thus making aclosed circuit. Gasoline vapors are withdrawn from the upper end ofdephlegmator I2 through line 2| to condensing coils 22l and then `tostorage tanks which are not shown.

It will be understood that the system thus far described is theconventional absorption system. It has been customary in using thesystem described above, to circulate the lighter components of newabsorption oil and the liqueiied heavier components of the absorbedgases or vapors remaining in the dephlegmator and designated as oilreflux, from the dephlegmator back to the still and dephlegmator again.

Instead of following the above conventional procedure, I have provided aline 23, shown in the drawing, from the lower end of dephlegmator I2 andleading back into absorber I at point 25 which is at a lower point inthe absorber than the inlet 3 for the Vlean oil. Interposed in this lineis a ycooler 24 and a pump 26 for pumping the oil reflux from thedephlegmator to the absorber.

The oil reux enters the absorber l at a point 25 below the top plate ofthe absorber. This point is chosen such that the composition of theabsorbent owing down through absorber at that point and the compositionof the oil reilux are similar with respect to the major heavyconstituents to be recovered from the gas. At the top of the absorber,ordinary stripped mineral seal oil (lean oil) enters and flows down thecolumn absorbing vapors or gases rising from the point at which the oilreux enters. At the point of entrance of the oil reux, the two streamsmerge and flow down the remainder of the column, becoming enriched withthe gas entering through line 2.

The rich oil then passes through pump 5, heat exchangers 6 and 1, venttank 8, preheater 9 and into steam still I0. In the still, the freedgasoline vapors or gases, light constituents of the mineral seal oilabsorbent and steam pass through the top as vapor to the dephlegmatorl2. The hot lean oil leaves the bottom of the still through line I3 andgoes through heat exchanger 1, surge tank I4, pump I6, heat exchanger E,cooler I1 and then to the top of the absorber. The heavier components ofthe freed vapors or gases and the light constituents of the mineral sealoil r other absorbent are condensed in the dephlegmator, the condensate,being the said oil reux, flows to the cooling coils 24 and is pumpedinto the absorber as absorbent again.

While I have shown my invention as embodied in specific form and asoperating in a speciiic manner for the purpose of illustration, itshould be understood that I do not limit my invention thereto, sincevarious modifications will suggest themselves to those skilled in theart without departing from the spirit of the invention, the scope ofwhich is set forth in the annexed claim.

I claim:

In the process of extracting heavier constituents from a mixture ofgases by selective absorption, the combination of steps comprisingintroducing absorbent oil to an absorber, contacting the gas with theabsorbent oil therein, steam distilling the resulting enriched absorbentoil, passing the vaporous effluent of the distilling step in contactwith water to dephlegmate the same to condense fractions having boilingpoints higher than water, separating the resulting condensate of thedephlegmating step from the water and passing the condensate to theabsorber at a point below that at which the absorbent oil is introduced.

GERALD W. MCCULLOUGH.

